This invention relates to pump assemblies and although it is especially useful in connection with fuel injection systems for internal combustion engines of various types it is also directed to new and novel pump systems of more general utility. Pump systems of the prior art have employed electromagnetic drives of various types but associated with each type there are serious disadvantages. Generally speaking, the prior art devices have been of complex nature and require electromagnetic devices for producing the requisite force or energy which are large and massive having regard to the volumetric output produced. Among other things, prior art pump electromagnetic drive devices which are large and massive not only present problems of economy in construction and are wasteful of space and energy but they also do not lend themselves well to high speed operation.
In many instances, the electromagnetic drives have required some type of return spring mechanism, which is fundamentally disadvantageous because the electromagnetic drive must dissipate some of its energy simply in wasteful opposition to the spring means and therefore must be larger and more powerful than otherwise would be the case. Examples of such drives may be found for example in Swiss Pat. No. 349,732, in French Pat. No. 1,108,288 in U.S. Pat. No. 3,380,387 and in German Pat. No. 598,918. Moreover, these devices utilize an armature which moves axially within the electromagnetic winding, inherently involving an inefficient flux field coupling which further augments the need for large electromagnets.
German Pat. No. 598,918 partially overcomes the inherent inefficiency associated with an axially shiftable armature by utilizing, in addition to and in conjunction with an axially shiftable armature, an external disc-like armature means which more efficiently couples the magnetic flux field and, moreover, achieves a characteristic wherein the force exerted on the armature increases during its stroke because the disc-like armature is approaching the electromagnet. However, the disc-like armature serves deleteriously to increase the total mass of the armature assembly, the system employs a return spring which has the disadvantages noted above and, moreover, the system requires the use of a compound piston arrangement to effect the fuel injection function. Further, the German patent requires the secondary piston of the compound piston arrangement to act also as the valve for the injector nozzle. Further, because the arrangement exemplified in devices of the type illustrated in the German patent inextricably combines the pumping and injecting spray functions it requires proximity of the electromagnetic drive mechanism with respect to the combustion cylinder. This is extremely disadvantageous because one cannot avoid excessive engine heat dissipation to the driving assembly and, as well, to the fuel in the pump chamber.
Other types of axial armatures, especially those involving pairs of pistons, as for example as shown in British Pat. No. 464,565, require correspondingly that one electromagnet be associated with each piston of each pair in order somewhat to overcome the inherent inefficiency of the axially located type of armature as noted in this patent. This patent also exemplifies a further prior art deficiency in that such axially reciprocating piston arrangements have been such that a continuous reciprocation is effected. To this end, switching means is coupled with pistion movement so that as soon as a piston reaches one end of its stroke the electromagnets are switched so as immediately to effect the return stroke. The inevitable result of such function is that the end of each pump delivery stroke is transient and therefore ill defined, that is to say, there is no time for the system to "settle" at the end of the delivery stroke. Particularly in systems where the pump operates at high speed, as would be required for a fuel injection system, and liquid delivery is done under high pressure over lines of appreciable length, the transient nature of the end of the stroke cycle will create substantial problems due to the dynamic forces acting on the fuel downstream of the pump. It is a practical impossibility to eliminate these dynamic problems by the use of check valves even though such check valves may have relatively rapid response both in opening and closing.
Generally speaking, the requirements for fuel injection systems are rather stringent, particularly if one is to achieve not only smooth engine response and fuel economy but also if one is to obtain emission characteristics which are acceptable by present day standards. It is essential that each charge delivered by the pump and as discharged at the injector be precise under all operating conditions of engine speed and load and that, as well, the pump discharge characteristics be such that the atomization achieved by the nozzle is effective to produce the proper spray pattern with consequent good ignitability and combustibility of the fuel/air mixture. With regard to these requirements, an axial type armature is inherently incapable of achieving same and even though arrangements such as in the German Pat. No. 598,918 partially overcome certain of the deficiencies of the prior art, there still is lacking complete compliance with all of the requirements which are essential to achieve an effective, efficient and non-polluting fuel injection system.
The above mentioned copending application Ser. No. 416,852 discloses a fuel injection system for internal combustion engines which represents substantial improvement over the prior art. In the copending application, the basic arrangement of a plate-like armature pivoted from one end and connected at its other end to a yoke carrying two pistons is shown. Between the pivot point and the connection to the yoke a pair of electromagnets are arranged on opposite sides of the armature, which electromagnets are energized alternately by means of monostable multivibrators. Because the electromagnets are located between the pivot point and the connection to the yoke, the gap between the electromagnets may be made very small while still achieving the requisite stroke of the pistons carried by the yoke. The fact that the armature is essentially perpendicular to the axes of the coils of the electromagnets produces the result that excellent magnetic flux field coupling is achieved with a minimum of armature mass. In consequence, taken in conjunction with the very small gap between the electromagents, each stroke of the armature is extremely rapid even when the electromagnets are small and compact and have relatively small inductance. The fact that the armature moves toward the electromagnet driving it results in an increasing force exerted on the liquid displacing element during its working stroke. Because of this and of the fact that each pump stroke is effected over a uniformly short time period regardless of engine speed, the spray pattern produced by the fuel atomizing nozzle is of improved form at all times. Said copending application, then, discloses the basic arrangement of a free-floating armature which is shuttled back and forth by electromagnetic means which are energized by pulse generator means, in combination with stop means which interrupt and delineate the end points of the movements of the pistons. The period of each injection cycle is totally independent of engine RPM allowing good ignition and combustion of stoichiometric fuel/air mixtures even at engine idling speed, which results in low CO emission. Further, the capability for remote location mounting assures that low charge temperature is inherent at the start of combustion which results in low NO.sub.x emission.